DE4447447C2 - Pacemaker - Google Patents

Description

The invention relates to a cardiac pacemaker the preamble of the main claim.

A large number of methods for adapting the stimulation frequency of cardiac pacemakers to the stress situation of the patient are known in the prior art. A distinction must be made between systems that use non-physiological parameters, such as movement (activity) of the body, and those systems that use physiological parameters of the body such as blood pressure or temperature for frequency control. Non-physiologically frequency-adapting systems have the disadvantage that they can lead to non-physiological stimulation frequencies (stair-up-stair-down paradox). Physiologically regulating sensors, on the other hand, have the disadvantage that they require special sensors in order to be able to measure suitable control parameters of the cardiovascular system, and these sensors do not have the required long-term stability. Therefore, there are a variety of me methodical approaches, including unspecific measurement methods that are carried out with long-term stable standard catheters, such as intracardiac impedance measurement, to make usable for pacemaker and defibrillator control. An essential feature of these approaches is that they use special methods to filter the signal content from the polymorphic signal, which in turn can be clearly assigned to physiologically definable processes. A distinction must be made between two concepts:

• 1. Passive measurement of intracardiac and intrathoraka ler measured values without targeted influencing of the Measurement section through the stimulator.
• 2. Active measurement of intracardiac measurement parameters with defined influencing of cardiovascular radio the stimulator.

Since actively measuring systems, for example by modulating the Stimulation frequency of the heart muscle, the advantage ha ben, through the phase-synchronous analysis, not cardiac To suppress disturbance variables, they are for use physiological function parameters for frequency stimulation preferred.

From US 5 360 436 a frequency control is one Activity cardiac pacemaker known in the one Variety of movement patterns and reaction patterns at different load levels with a ge healthy person measured and placed in a pacemaker get saved. The stress levels of the person Having a pacemaker is about an activity sensor, d. H. a mechanical not physiological Sensor detected and ver with the pulse rate of the pattern that was on best matches to control the pacemaker chers is used.

Physiological sensors are also mentioned, but no indication is given as to how such Senso are to be applied.

The invention is based on the object of a heart to create a pacemaker that does not require function-specific signal components from an intra To filter out cardiac mixed measurement signal, exactly and quickly grasps the physical stress level and accordingly the basic frequency of the stimulation controls.

According to the invention, this object is achieved by the characteristic Characteristics of the main claim in connection solved with the features of the generic term.

The pacemaker according to the invention avoids the problem of Filtering of individual function-specific signals parts of a mixed signal, such as the intracardial one Impedance by relying on an exact discrimination ver is renounced and instead only consequences of definite th signal parameters are analyzed, which are based on a exactly reproducible way on certain influencing variables such as physical exertion and pulse frequency of the heart react, so that each value sequence ge a certain load and frequency dependent Has course characteristic. This results in the possibility of saving a corresponding Number of these value sequences with defined loads as a reference value field by comparing one or more rer current value sequences with the saved Values to detect the prevailing degree of exposure For this purpose, the stored sequence of values is determined represents, based on the respective base frequency has the greatest correlation to the current sequence of values. This procedure then does not require a precise ana analysis of individual signal content typical of exposure more.

In the pacemaker according to the invention will each previously selected combination of defi nated stress condition and pulse rate a reference assigned to a limit value field in which an associated fol ge of signal parameters of physiological measurement signals can be saved. These saved values who which is then used as a reference value (sample template), by comparing it with current measurement signal sequences or patterns of different stressful situations to detect. The procedural principle used here the identification of course characteristics or Progress patterns of physiological measured values is accordingly, the more effective, the more interference-free the ever certain sequences of values can be reproduced and the more characteristic their course is. The right one producible value pattern or the reference value field are won by the respective set Sti mulation frequency is modulated and as Signalpara meter only the signal components are used that are passed through the frequency modulation can be influenced so that due to the demodulation non-modulation-synchronous Disturbance variables are suppressed. An exemplary one Form of obtaining a sequence of signal parameters, is different types and degrees of Perform frequency modulation, whereupon at closing demodulation a correspondingly large Number or sequence of values can be obtained.

By the measure specified in the subclaims men are further improvements and further training possible. It is particularly advantageous that a fast and precise regulation of the stimulation frequency on the respective load condition can be made.

An embodiment of the invention is in Drawing and is shown in the following Description explained in more detail. Show it:

Fig. 1 shows a time course of the modulier th stimulation frequency under different basic frequencies and un ferent degrees of modulation with double pulse modulation as a type of modulation,

Fig. 2 is a reference value field as stress stimulation frequency coordinate field with different fundamental frequencies and different stress levels,

Fig. 3 shows the representation of a signal parameter Fig. 3a after a frequency change corresponding to different degrees of modulation or sampling times within the pulse interval,

4 shows a block diagram of a device according to an exemplary embodiment of the present invention, and FIG

Fig. 5 is a block diagram of a device according to a further Ausführungsbei game of the present invention.

In Fig. 4 is a block diagram of a heart pacemaker is shown, which is controlled depending on stimulation pulses with a predefinable stimulation frequency. The pacemaker contains a stimulation pulse generator 3 which is connected to one or more electrodes 1 arranged in the patient's heart. The stimulation pulse generator 3 is connected to a control stage 4 , which controls the size and time sequence, that is, the frequency of the stimulation pulses. The stimulation electrodes 1 are used at the same time as measuring electrodes for EKG and impedance measurement, it being possible for additional sensors 2 (for example for measuring pressure or oxygen content) to be integrated in the catheter. The electrodes or sensors 1 , 2 are connected to a processing and evaluation unit 14 in which the signals supplied by the electrodes 1 or sensors 2 are processed and evaluated, as will be described later. The processing and evaluation unit 14 is connected to a standardized process control 12 and a telemetry device 13 , the data from the processing unit 14 to the outside and vice versa. The pacemaker is controlled via the stimulation electrode 1 with a stimulation frequency predetermined by the Re gel stage 4 , whereby stimulation pulses are delivered to the heart. This frequency is set by the control stage depending on different setting parameters. Table 1 lists the most common setting parameters of the stimulation frequency (HR ₀ ) and their changes (ΔHR _j ), from which, depending on the application, certain combination sequences or patterns can be put together. In the bottom row of Table 1, the number of a normal combination and in brackets that of the maximum combination cases is given.

Table 1

With the type of stimulation SM, a basic distinction must be made between intrinsic rhythm (SINUS) and artificial stimulation, which in turn is separated into the atrium (A), ventricle (V) and the combined AV stimulation. Only four values are initially determined as the basic values (basic frequency HR ₀ ) of the stimulation frequency, each selected from a value range which in turn is assigned to one of the stress ranges defined below. In the case of sinus rhythm, the respective mean pulse frequency of several (<4) consecutive pulses is calculated as a reference variable and assigned to one of the four frequency ranges.

As is known from the prior art, the latter is modulated for frequency regulation of the stimulation frequency and the reactions of the intracardiac signals to this modulation are recorded and evaluated, for example via the EKG measurement. The type of frequency modulation and the degree of frequency modulation or both can be changed. According to Table 1, a distinction is made between the types of modulation, for example, only between typical forms of single pulse modulation, in which the interval between two consecutive pulses is either lengthened (-ΔHR _j ) or shortened (+ ΔHR _j ) at periodic intervals of n pulses. Of course, other types of frequency modulation can also be considered; for the sake of simplicity, the exemplary embodiment relates to double pulse modulation.

In Table 1, the degree of frequency modulation is given as a percentage, the reference variable being the basic frequency HR _{0 of} the stimulation pulses. For the gradual setting of the degree of modulation, shortening or lengthening of the pulse interval were selected, which correspond to a frequency difference of ± 5, 10 and 20%.

Table 2 shows the setting parameters for the physical stress P _k . Various types of physical stress are listed as examples that are used in the medical field for evaluating body functions as reproducible stress conditions. Different degrees of physical stress a) to d) can be assigned to each type of physical exertion. Accordingly, load settings of this type in conjunction with defined frequency modulations can provide reference values that are required for general load detection in pacemakers. The degree of physical stress is an individually variable variable, so the maximum power level (N _max ) must first be determined for the individual ne person, which serves as a reference value for example for two further stress levels with 1/3 and 2/3 N _max .

Table 2

The basis of the idea of the invention is that for an individual person normal stress levels or levels and under different stimulation frequencies who are saved those that serve as reference value fields and with those current measured values are compared, with the Er result of the comparison for the control or regulation the pacing rate can be used. Included can be the type of underlying the measured values intracardiac signals can be chosen arbitrarily, it only have to use the same signal parameters for the Reference value fields and the current measured values be used.

The type of creation of the reference value fields is explained in more detail below. Table 3 shows an exercise-stimulation frequency (base frequency) coordinate field (HR-P coordinate field), with each coordinate point, which is determined by a stress level (P _k ) and a base value of the stimulation _{frequency (HR 0} ), a sequence of Measured values M _ik (ΔHR _j ) is assigned. The sequence of measured values, ie of intracardial measurement signals, is determined as a function of the respective degree of frequency modulation (ΔHR _j ). This results in the value arrangement compiled in Table 3 as an example.

Table 3

To determine the reference value field in the present exemplary embodiment, an HR-P coordinate field with four basic values (HR ₀ ) for the stimulation frequency, which is generally referred to as the pulse frequency, and four values (P _k ) for the physical stress situation is determined, which results in 16 event fields. A sequence of measured values M _{ik is} assigned to each of these fields, which in the present case are calculated as a function of various levels of frequency modulation (ΔHR _j).

On the one hand, a constant type of modulation is used as frequency modulation, in which a combination of an equally large positive and negative frequency change of two successive pulse intervals (double pulse modulation) is selected, and on the other hand, three different degrees of modulation of 5, 10 and 20% are used. Each frequency change is repeated after a certain number of pulses in order to be able to form an average value over a certain number of pulses (m), with a modulation level of 5% a number m ₅ = 16, with a modulation level of 10% m ₁₀ = 12 and with a degree of modulation of 20% m ₂₀ = 8 is selected.

If two unmodulated pulse intervals (HR = HR ₀ ) are used between the individual degrees of double pulse modulation, then the time course of the modulated stimulation or pulse frequency shown in FIG. _{1 results with two different basic values HR 0} (70 and 90 pulses / min). As can be seen from Fig. 1, the lower modulier th pulse intervals have a higher repetition frequency because signal changes with a low degree of modulation have a lower signal-to-noise ratio and should accordingly be integrated over a higher number of pulses. In addition, in the example shown, repetition frequencies are sto chastically variable in a certain range in order to prevent interference with periodic influencing variables on the intracardiac measurement signal, such as breathing.

In the described and illustrated embodiment, _{the impedance is selected as the ΔHR j} -dependent signal parameter, namely the mean normalized value α _{ik of} the maximum impedance change ΔZ _max during a pulse interval (n + 1) after the interval change of the pulse (n). The mean value ΔZ _max was calculated depending on the different repetition frequencies over, for example, m ₅ = 16, m ₁₀ = 12 and m ₂₀ = 8 (m number of pulses). This results in the respective mean value:

with

ΔZ_{max (n)} = Z_{max (n)} - Z_{min (n)}. As a normalized value

α _ik is z. B. the quotient is calculated from the difference between the ΔZ _max value of the respective pulse (n + 1), which is influenced by the frequency change (ΔHR _j ) of the previous pulse interval (n), and a reference value (ΔZ _0max ) which is not influenced by a change in frequency according _{to ΔZ 0max:}

α _ik (ΔHR _j ) = (ΔZ _max - ΔZ _0max ) / ΔZ _0max .

In Fig. 2 an HR-P coordinate field corresponding to Table 3 is shown as a reference value field of characteri tical measured value sequences, which are designed as normalized α _ik (ΔHR _j ) sequences. The value sequences of 6 ΔHR-dependent signal parameters α _ik after frequency changes with a degree of modulation MIR of +/- 5, 10, 20%, were load levels at four different base frequencies (70, 90, 120, 150 pulses / min) and four loading levels (P1-P4) determined according to Table 2. The value sequence α ₃₁ at a fundamental frequency of 120 pulses / min in the idle state is shown enlarged in Fig. 3, the deviations in the different degrees of modulation can be clearly seen.

A reference value field, as shown in Fig. 2, can be stored person-specifically, where, of course, additional fields with different Parame tern both with regard to the frequency modulation and the load as well as the detected signal parameters can be stored in its place.

According to the exemplary embodiment, the value patterns are selected from the reference value field according to FIG. 2 during the defined stress tests, ie during the reference measurement, which result from the respective stimulation frequencies assessed as being optimal.

A physiologically optimal relationship between load and stimulation frequency is given by the equation

HRo = HR _min , + cP _k

where HRo is the basic frequency and HR _min and c are individually adjustable constants. This results in a change pattern defined as optimally for each basic frequency HRo corresponding to the characteristic curve 15 shown in dashed lines in FIG. 2, that is to say four reference value patterns for four basic frequencies. These reference value patterns are specified specifically for each person. If it proves to be advantageous for the patient, other reference value patterns can also be selected from the entire reference value field that are appropriate to his physical condition.

To determine the current, unknown physical stress level of the person wearing the pacemaker, a standardized sequence of measured values α _ik at a given base frequency and with a type of frequency modulation and the various degrees of modulation is determined by measurement and calculation, as is the case with the reference measurement. In principle, any identification method is suitable for determining the physical stress levels with the aid of the currently measured MIR-related sequence of values, with so-called optimal value filtering being described in the exemplary embodiment. The square of the mean difference (Δα _ik ) ² between the values of the current measurement sequence and those of the reference value sequences is determined and the sum ρ _{ik of} all values determined in this way is calculated:

In general, the coordinate point for which ρ _{ik is} the smallest defines the current sequence of measured values that correlates best with the sequence of reference values and thus characterizes the respective degree of exposure, ie:

P _k = P _k (ρ _ik → min).

If ρ _{ik is} above a certain threshold value, the regulation is carried out and the basic frequency is increased or decreased in _{accordance with the value ρ ik and α ik is} measured and compared with the next higher or lower reference value pattern. As a result, the optimal basic frequency for the current load is set according to the stored patterns.

The device performing the processing operation described above is shown in FIG. 4, the control stage 4 controlling the stimulation pulse generator with regard to the size and time sequence (frequency of the stimulation pulses) which are passed on to the stimulation electrodes.

The device for processing and evaluation 14 includes all for processing the measurement signals derived from the measuring or electrode arrangement 1 , 2 he required functional stages. These essentially include a preamplifier 5 with A / D converter, signal preprocessing 6 that is not pulse interval-related, ie, stimulation frequency-related, and pulse interval-triggered signal processing 7 . When the pulse interval is changed, the frequency control stage 4 sends a trigger pulse to the processing stage 7 , which then calculates the mean value. A subsequent signal analysis stage 8 detects the pulse interval-related values of the averaged Signalver courses, which are most characteristic for the analysis required, such as the maximum amplitude change in intracardiac impedance per pulse interval. The signal analysis stage 8 is followed by a SpeI cherstufe, being stored in the tefelder Speicherbe rich 9 a reference value field, or the Referenzwer and in the memory area 9, the current Meßwertefolgen b cached who the. A comparison stage 10 analyzes the correlation ρ _ik between the reference value fields and the current measured value sequences and forwards the result to the frequency control stage 11 . The basic value HR _{0 of} the stimulation frequency determined by the frequency control stage as a function of the correlation factor ρ _ik controls the pulse interval generator 4 in combination with the process controller 12 , which in turn determines the duration, type and degree of frequency modulation according to a program that can be specified via telemetry 13.

In the exemplary embodiment described above, the measured value sequences with the shape shown in FIG. 2 were determined on the basis of the impedance measurement. However, other measurement parameters or combined parameters can also be selected, in which case a reference value field corresponding to FIG. 2 is then based on other curve forms.

The adaptation of the pacemaker to changed load conditions is relatively slow, since the reactions must be awaited for the modulation and the measuring cycle is relatively long. This can be improved by a combination with a movement-dependent sensor according to FIG. 5.

Movement-dependent sensors are used in activity pacemakers, but they have the functional len disadvantage that they are in principle influenced by non-physiological variables (acceleration, vibrations) and react unspecifically. The load detection according to FIG. 5 enables a correction of non-physiological changes in the stimulation frequency.

In Fig. 5, 20 designates a motion sensor, designed for example as a piezo element, which is connected to a signal evaluation stage 21 , the output of which is connected to a comparator / switch 22 which is connected to the pulse interval generator or modulator 4 , which controls the stimulation pulse generator 3 controls. The stimulation pulses are fed to the stimulation electrodes 1.

In parallel, the arrangement described above is effective, that is, the impedance is measured via the impedance measuring electrodes 2 and fed to the signal processing stage 14 , which processes the recorded measurement parameters, here the impedance in comparison with the stored reference values described above, and the appropriate stimulation frequency HR _b calculated as a function of the current impedance values.

The operation of the device according to FIG. 5 is as follows.

Normally, the basic frequency HR _{b is} continuously detected via the impedance measuring electrodes 2 and the signal processing stage 14 without performing the modulation, and the stimulation pulse generator 3 is controlled accordingly.

If the motion sensor 20 detects a changed movement, in the signal evaluation 21 is Festge represents whether the change is above a predetermined threshold, and according to the known prior art to the movement of a Grundfre frequency HR _a set. In the comparator / switch 22 it is determined whether this fundamental frequency is greater or less than the fundamental frequency HR _b , which is continuously detected by the impedance measuring device.

If this is the case, a signal is provided to Pulsintervallge about 4 given a modulation HR = HR _b + perform ΔHR wherein represents Stimulationspulsgenera gate 3 outputs the respective pulses, and it is a scheme similar to that in connection with FIGS. 1 to 4 carried out the description. In the comparator 22 it is determined whether the basic frequency HR _b determined via the signal processing stage 14 corresponds to the frequency HR _a determined as a function of the motion sensor 20. If the change in movement was caused by non-physiological variables, then the pulse interval generator 4 changes the basic frequency to the value HR _b set via the impedance. Otherwise, the basic frequency HR _{a is} specified and the modulation is ended.

In the example according to FIGS. 2 and 3, the reference value field is formed by measured impedance values that were detected using a type of modulation at different fundamental frequencies and degrees of modulation and under different load levels, whereby a "two-dimensional" measured value field is formed. It is also possible to select a "three-dimensional" measured value field by using, for example, a variable type of modulation as an additional parameter.

It is conceivable that at assume the varying degrees of modulation different sampling times within the pulse sinter valls are recorded. The accuracy of the correla tion analysis improves with the number of records th characteristic measured values. This means that to create the sequence of measured values either the number the degree of modulation must be increased or the pro Degree of modulation recorded measured values. Since it is physiologi What is more important is the number and size of the modules used to keep the degree of movement as small as possible in order to maintain the natural The modulation range of the pulse frequency is as little as possible to exceed, the fact should be used that the stimulus spread as well as pressure-volume- Function of the heart four characteristic phases goes through, each specific by the Fre frequency modulation can be influenced. Accordingly it is useful for intracardiac measured values that like the impedance from the pressure or volume curve hang, at least two per recorded pulse interval Measured values, e.g. B. Maximum during systole and minimum during diastole, to measure.

In practice it is more advantageous to reduce the effort for to bypass pulse phase-specific sampling and instead, the measurement signal at a fixed time points during the pulse interval.

For example, if the frequency modulation with only one degree of modulation of z. B. +/- 10% is carried out, but z. If, for example, six sampling times are used within the pulse interval, the result is analogous to FIG. 3 of the sequence of measured values according to FIG. 3a.

Claims (11)

1. Pacemaker
with stimulation electrodes to stimulate the heart with pulses of a variable basic frequency,
with a sensor device for detecting the measured values relating to the cardiac function and with a device for processing and evaluating the same, which has a memory for storing a predetermined reference value field that takes into account the physical load, the basic frequency being changed using the reference value field, thereby marked ,
that a device for modulating the basic frequency with at least one type of modulation and with at least one degree of modulation is available,
that the sensor device ( 1 , 2 ) at different predeterminable levels (P _k ) of physical stress at different predefinable basic values (HR ₀ ) of the stimulation frequency, with at least one type of modulation of the stimulation frequency and different predeterminable degrees of modulation of the stimulation frequency each Weil at least one intracardiac measured value Signals are recorded and the resulting measured value _sequences are stored as a reference value field (α ikref) in the memory,
that the sensor device ( 1 , 2 ) measures current intracardiac signals at one of the basic frequencies of the stimulation pulses and the type of modulation and the predetermined different degrees of modulation of the stimulation frequency as a measured value sequence (α _ik ),
that the device for processing and evaluation ( 14 ) correlates the current sequence of measured values with the sequence of measured values stored as a reference value field, the load level of that sequence of measured values in the reference value field being determined as the current load level which has the greatest correlation to the current sequence of measured values and that the fundamental frequency is changed accordingly. 2. Cardiac pacemaker according to claim 1, characterized in that the setting of the basic frequency of the stimulation pulses according to a predetermined characteristic curve ( 15 ) of the basic frequency is made as a function of the load or according to predetermined person-specific reference values pattern. 3. A pacemaker according to claim 1, characterized in that the stimulation _{frequency is modulated in such a way that the time interval (Δt M} ) between only two successive stimulation pulses is shortened or lengthened compared to a mean interval defined as a base value and that this process is periodic is repeated after a certain number (m) of pulses. 4. Cardiac pacemaker according to one of claims 1 to 3, characterized in that as intracardia les measuring signal the voltages are selected that without (EKG) and / or with power supply (impedance) via the electrodes of unipolar or multi-pole stimu lation catheter are divertable. 5. Cardiac pacemaker according to one of claims 1 to 4, characterized in that the extreme values of the intracardiac signal or its first Ab conduction within a systolic or dia stolic time interval or the time from stand between the start of the stimulation pulse ses and reaching one of the extreme values be chosen. 6. Cardiac pacemaker according to one of claims 1 to 5, characterized in that as a frequency module lation-dependent measured variable the changes in the ever because the intracardiac measurement signal was used resulting from the analysis of the Sig nal course during the interval change result in the following two pulse intervals, where either the difference between the base value and the value affected by the modulation during one and / or the other pulsin tervalls or those relating to the basic value normalized change value is determined. 7. Cardiac pacemaker according to one of claims 1 to 6, characterized in that the mean value of the change value used in each case over meh rere change periods is determined. 8. Cardiac pacemaker according to one of claims 1 to 7, characterized in that the modulation the pacing rate with processing and evaluation of the measurement signals in certain Time intervals takes effect that depend on the evaluation of one or more additional, measured parameters detected in the pacemaker will be started. 9. pacemaker according to claim 8, characterized ge indicates that the additional measurement parameter not directly related to the cardiovascular function of the Body is coupled and unphysiologically rea greed. 10. pacemaker according to claim 9, characterized ge indicates that the body movement of one Motion sensor is detected. 11. Cardiac pacemaker according to one of claims 8 to 10, characterized in that upon detection of the additional measurement parameter is the modulation and the evaluation with the help of the from the Fre frequency modulation dependent reference pattern is performed, and a comparison of the so found nen base frequency with a base frequency that due to the evaluation of the additional measuring pa rameters is determined is performed.